Composite metal oxide particles

ABSTRACT

A powder of lithiated manganese oxide has an average particle diameter preferably less than about 250 nm. The particles have a high degree of uniformity and preferably a very narrow particle size distribution. The lithiated manganese oxide can be produce by the reaction of an aerosol where the aerosol comprises both a first metal (lithium) precursor and a second metal (manganese) precursor. Preferably, the reaction involves laser pyrolysis where the reaction is driven by heat absorbed from an intense laser beam.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to copending U.S. patentapplication Ser. No. 09/188,768, now U.S. Pat. No. ______, to Kumar etal., entitled “Composite Metal Oxide Particles,” incorporated herein byreference.

FIELD OF THE INVENTION

[0002] The invention relates to composite metal oxide powders. Moreparticularly, the invention relates to highly uniform, nanoscalecomposite metal oxide particles, such as lithiated manganese oxide,produced by laser pyrolysis.

BACKGROUND OF THE INVENTION

[0003] Manganese can exist in various oxidation states. Correspondingly,manganese oxides are known to exist with various stoichiometries. Inaddition, manganese oxides with a particular stoichiometry can havevarious crystalline lattices, or they can be amorphous. Thus, manganeseoxides exhibit an extraordinarily rich phase diagram. Variouscrystalline forms of manganese oxide, as well as other metal oxides, canaccommodate lithium atoms and/or ions into its lattice.

[0004] The ability of metal oxide, such as manganese oxide, tointercalate lithium can be used advantageously for the production oflithium and lithium ion batteries. In particular, LixMn₂O₄, 0<x<2 can beused in the formation of cathodes for secondary batteries, i.e.,rechargeable batteries. These are referred to as “rocking-chair”batteries by their ability to reversibly vary x between certain valuesas the battery charges or discharges. The lithiated manganese oxides canhave a variety of crystal structures. Because of the interest inlithiated manganese oxides and other composite metal oxides, there isconsiderable interest in developing better approaches for producingcomposite metal oxides, such as lithiated manganese oxide.

SUMMARY OF THE INVENTION

[0005] In a first aspect, the invention pertains to a method ofproducing a composite metal oxide particles, the method comprisingreacting an aerosol to form a powder of composite metal oxide particleswith an average diameter less than about one micron, the aerosolcomprising a first metal compound precursor and a second metal compoundprecursor.

[0006] In a further aspect, the invention pertains to a method forproducing lithium metal oxide, the method comprising pyrolyzing areactant stream in a reaction chamber, the reactant stream comprising alithium precursor, a non-lithium metal precursor, an oxidizing agent,and an infrared absorber, where the pyrolysis is driven by heat absorbedfrom a light beam.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a schematic, sectional view of an embodiment of a laserpyrolysis apparatus taken through the middle of the laser radiationpath. The upper insert is a bottom view of the injection nozzle, and thelower insert is a top view of the collection nozzle.

[0008]FIG. 2 is schematic, side view of a reactant delivery apparatusfor the delivery of an aerosol reactant to the laser pyrolysis apparatusof FIG. 1.

[0009]FIG. 3 is a schematic, perspective view of an elongated reactionchamber for the performance of laser pyrolysis, where components of thereaction chamber are shown as transparent to reveal internal structure.

[0010]FIG. 4 is a perspective view of an embodiment of an elongatedreaction chamber for performing laser pyrolysis.

[0011]FIG. 5 is a sectional, side view of a reactant delivery apparatusfor the delivery of an aerosol reactant into the reaction chamber ofFIG. 4, where the section is taken through the center of the reactantdelivery apparatus.

[0012]FIG. 6 is a schematic, sectional view of an oven for heatingnanoparticles, in which the section is taken through the center of thequartz tube.

[0013]FIG. 7 is an x-ray diffractogram of nanoparticles of lithiatedmanganese oxide produced by laser pyrolysis of a reactant stream with anaerosol.

[0014]FIG. 8 is an x-ray diffractogram of nanoparticles of lithiatedmanganese oxide following heating in an oven.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Lithiated manganese oxide particles having diameterssubstantially less than a micron have been produced directly by laserpyrolysis. Laser pyrolysis with an aerosol based reactant deliveryprovides for the direct production of lithium/manganese compositematerials. Lithiated manganese oxide nanoparticles preferably areproduced by laser pyrolysis with a relatively high production rate. Heatprocessing of the composite materials results in crystalline lithiatedmanganese oxide particles. The small size of the particles results in asignificantly increased surface area for a given weight of material. Theaerosol based approach described herein can be used for the productionof other composite metal oxides, in particular other lithiated metaloxides such as lithiated vanadium oxides.

[0016] Preferred collections of composite metal oxide particles have anaverage diameter less than a micron and a very narrow distribution ofparticle diameters. Furthermore, the collection of composite metaloxides preferably are very uniform. In particular, the distribution ofparticle diameters preferably does not have a tail. In other words,there are effectively no particles with a diameter significantly greaterthan the average diameter such that the particle size distributionrapidly drops to zero.

[0017] To generate the desired nanoparticles, laser pyrolysis is usedeither alone or in combination with additional processing. Specifically,laser pyrolysis has been found to be an excellent process forefficiently producing lithiated manganese oxide nanoparticles with anarrow distribution of average particle diameters. In addition,nanoscale lithiated manganese oxide particles produced by laserpyrolysis can be subjected to heating in an oxygen environment or aninert environment to alter the crystal properties of the lithiatedmanganese oxide particles without destroying the nanoparticle size.

[0018] A basic feature of successful application of laser pyrolysis forthe production of composite metal oxide (lithiated manganese oxide)nanoparticles is production of a reactant stream containing a firstmetal (e.g., lithium) precursor, a second metal (e.g., manganese)precursor, a radiation absorber and an oxygen source. The second metalprecursor involves a different metal than the first metal precursor. Inpreferred embodiments, the first metal (lithium) precursor and/or thesecond metal (manganese) precursor are supplied as an aqueous solutionor solutions that are formed in an aerosol and injected into thepyrolysis chamber using an ultrasonic nozzle. The novel injection systemfor the laser pyrolysis instrument is described in greater detail below.Additional metal precursors can be included to produce ternary andhigher metal particles.

[0019] The reactant stream is pyrolyzed by an intense laser beam. Theintense heat resulting from the absorption of the laser radiationinduces the oxidation of the first metal (lithium) precursor, secondmetal (manganese) precursor, any additional metal precursors in theoxidizing environment. The laser pyrolysis provides for formation ofphases of materials that are difficult to form under thermodynamicequilibrium conditions. As the reactant stream leaves the laser beam,the composite metal oxide particles are rapidly quenched.

[0020] As noted above, lithium atoms and/or ions can intercalate intovarious forms of manganese oxide. The result is lithiated manganeseoxide. As described herein, lithiated manganese oxide is formed directlyas a composite. The lithiated manganese oxide nanoparticles can beincorporated into a film with a binder such as a polymer. The filmpreferably incorporates additional electrically conductive particlesheld by a binder along with the lithiated manganese oxide particles. Thefilm can be used as a cathode in a lithium battery or a lithium ionbattery.

[0021] A. Particle Production

[0022] Laser pyrolysis has been discovered to be a valuable tool for thedirect production of nanoscale lithiated manganese oxide particles andcomposite metal oxides, generally. In addition, the particles producedby laser pyrolysis are a convenient material for further processing toexpand the pathways for the production of desirable composite metaloxide particles and to improve the particle properties. Thus, usinglaser pyrolysis alone or in combination with additional processes, awide variety of composite metal oxide particles can be produced.

[0023] The reaction conditions determine the qualities of the particlesproduced by laser pyrolysis. The reaction conditions for laser pyrolysiscan be controlled relatively precisely in order to produce particleswith desired properties. The appropriate reaction conditions to producea certain type of particles generally depend on the design of theparticular apparatus. Specific conditions used to produce lithiatedmanganese oxide particles in a particular apparatus are described belowin the Examples. Furthermore, some general observations on therelationship between reaction conditions and the resulting particles canbe made.

[0024] Increasing the laser power results in increased reactiontemperatures in the reaction region as well as a faster quenching rate.A rapid quenching rate tends to favor production of high energy phases,which may not be obtained with processes near thermal equilibrium.Similarly, increasing the chamber pressure also tends to favor theproduction of higher energy structures. Also, increasing theconcentration of the reactant serving as the oxygen source in thereactant stream favors the production of particles with increasedamounts of oxygen.

[0025] Reactant gas flow rate and velocity of the reactant gas streamare inversely related to particle size so that increasing the reactantgas flow rate or velocity tends to result in smaller particle size.Also, the growth dynamics of the particles have a significant influenceon the size of the resulting particles. In other words, different formsof a product compound have a tendency to form different size particlesfrom other phases under relatively similar conditions. Laser power alsoinfluences particle size with increased laser power favoring largerparticle formation for lower melting materials and smaller particleformation for higher melting materials.

[0026] Laser pyrolysis has been performed generally with gas phasereactants. The use of exclusively gas phase reactants is somewhatlimiting with respect to the types of precursor compounds that can beused. Thus, techniques have been developed to introduce aerosolscontaining reactant precursors into laser pyrolysis chambers. Theaerosol atomizers can be broadly classified as ultrasonic atomizers,which use an ultrasonic transducer to form the aerosol, or as mechanicalatomizers, which use energy from one or more flowing fluids (liquids,gases, or supercritical fluids) themselves to form the aerosol.

[0027] Furthermore, as described herein, aerosol based approaches can beused to produce metal composite particles by the introduction ofmultiple metal compounds into a solution to be delivered as an aerosolin the reaction chamber. Improved aerosol delivery apparatuses forreactant systems are described further in commonly assigned andsimultaneously filed U.S. patent application Ser. No. 09/188,670, nowU.S. Pat. No. 6,193,936 to Gardner et al., entitled “Reactant DeliveryApparatuses,” incorporated herein by reference. If desired, selectedmetal precursors can be delivered in the reaction chamber as an aerosolwhile others are delivered as a vapor.

[0028] Using aerosol delivery apparatuses, solid precursor compounds canbe delivered by dissolving the compounds in a solvent. Alternatively,powdered precursor compounds can be dispersed in a liquid\solvent foraerosol delivery. Liquid precursor compounds can be delivered as anaerosol from a neat liquid, a liquid/gas mixture or a liquid solution,if desired. Aerosol reactants can be used to obtain significant reactantthroughput. The solvent, if any, can be selected to achieve desiredproperties of the solution. Suitable solvents include water, methanol,ethanol and other organic solvents. The solvent should have a desiredlevel of purity such that the resulting particles have a desired puritylevel.

[0029] If the aerosol precursors are formed with a solvent present, thesolvent is rapidly evaporated by the laser beam in the reaction chambersuch that a gas phase reaction can take place. Thus, the fundamentalfeatures of the laser pyrolysis reaction is unchanged. However, thereaction conditions are affected by the presence of the aerosol. Below,examples are described for the production of lithiated manganese oxidenanoparticles using aerosol precursors using a particular laserpyrolysis reaction chamber. The parameters associated with aerosolreactant delivery can be explored fully based on the description below.

[0030] A number of suitable solid, manganese precursor compounds can bedelivered as an aerosol from solution. For example, manganese chloride(MnCl₂) is soluble in water and alcohols and manganese nitrate(Mn(NO₃)₂) is soluble in water and certain organic solvents. Similarly,as substitutes for the manganese precursors, suitable vanadiumprecursors include, for example, VOCl₂, which is soluble in absolutealcohol. Also, suitable lithium precursors for aerosol delivery fromsolution include, for example, lithium chloride (LiCl), which issomewhat soluble in water, alcohol and some other organic solvents, andlithium nitrate (LiNO₃), which is somewhat soluble in water and alcohol.

[0031] The compounds are dissolved in a solution preferably with aconcentration greater than about 0.5 molar. Generally, the greater theconcentration of precursor in the solution the greater the throughput ofreactant through the reaction chamber. As the concentration increases,however, the solution can become more viscous such that the aerosol hasdroplets with larger sizes than desired. Thus, selection of solutionconcentration can involve a balance of factors in the determination of apreferred solution concentration. In the formation of compositeparticles, the relative amounts of the metal precursors also influencesthe relative amount of the metals in the resulting particles. Thus, therelative amounts of different metal precursors is selected to yield adesired product particle composition.

[0032] Preferred reactants serving as oxygen source include, forexample, O₂, CO, CO₂, O₃ and mixtures thereof. The reactant compoundfrom the oxygen source should not react significantly with the manganeseor lithium precursor prior to entering the reaction zone since thisgenerally would result in the formation of large particles.

[0033] Laser pyrolysis can be performed with a variety of optical laserfrequencies. Preferred lasers operate in the infrared portion of theelectromagnetic spectrum. CO₂ lasers are particularly preferred sourcesof laser light. Infrared absorbers for inclusion in the molecular streaminclude, for example, C₂H₄, NH₃, SF₆, SiH₄ and O₃. O₃ can act as both aninfrared absorber and as an oxygen source. The radiation absorber, suchas the infrared absorber, absorbs energy from the radiation beam anddistributes the energy to the other reactants to drive the pyrolysis.

[0034] Preferably, the energy absorbed from the radiation beam increasesthe temperature at a tremendous rate, many times the rate that heatgenerally would be produced even by strongly exothermic reactions undercontrolled condition. While the process generally involvesnonequilibrium conditions, the temperature can be describedapproximately based on the energy in the absorbing region. The laserpyrolysis process is qualitatively different from the process in acombustion reactor where an energy source initiates a reaction, but thereaction is driven by energy given off by an exothermic reaction.

[0035] An inert shielding gas can be used to reduce the amount ofreactant and product molecules contacting the reactant chambercomponents. Appropriate shielding gases include, for example, Ar, He andN₂.

[0036] An appropriate laser pyrolysis apparatus generally includes areaction chamber isolated from the ambient environment. A reactant inletconnected to a reactant supply system produces a reactant stream throughthe reaction chamber. A laser beam path intersects the reactant streamat a reaction zone. The reactant/product stream continues after thereaction zone to an outlet, where the reactant/product stream exits thereaction chamber and passes into a collection system. Generally, thelaser is located external to the reaction chamber, and the laser beamenters the reaction chamber through an appropriate window.

[0037] Referring to FIG. 1, a particular embodiment 100 of a pyrolysisapparatus involves a reactant supply system 102, reaction chamber 104,collection system 106, laser 108 and shielding gas delivery system 110.Reactant supply system 102 is used to deliver one or more reactants asan aerosol.

[0038] Referring to FIG. 2, reactant supply system 102 is used to supplyan aerosol to duct 132. Duct 132 connects with rectangular channel 134,which forms part of an injection nozzle for directing reactants into thereaction chamber. Reactant supply system 102 includes a delivery tube152 that is connected to duct 132. Venturi tube 154 connects to deliverytube 152 as a source of the aerosol. Venturi tube 154 is connected togas supply tube 156 and liquid supply tube 158.

[0039] Gas supply tube 156 is connected to gas source 160. Gas source160 can include a plurality of gas containers that are connected todeliver a selected gas mixture to gas supply tube 156. The flow of gasfrom gas source 160 to gas supply tube 156 is controlled by one or morevalves 162. Liquid supply tube 158 is connected to liquid supply 164.Delivery tube 152 also connects with drain 166 that flows to reservoir168.

[0040] In operation, gas flow through venturi tube 154 creates suctionthat draws liquid into venturi tube 154 from liquid supply tube 158. Thegas liquid mixture in venturi tube 154 forms an aerosol when venturitube 154 opens into delivery tube 152. The aerosol is drawn up into duct132 by pressure within the system. Any aerosol that condenses withindelivery tube 152 is collected in reservoir 168, which is part of theclosed system. Suitable venturi based aerosol generators for attachmentto duct 132 include, for example, model 3076 from the ParticleInstrument Division, TSI Inc., Saint Paul, Minn.

[0041] Referring to FIG. 1, shielding gas delivery system 110 includesinert gas source 190 connected to an inert gas duct 192. Inert gas duct192 flows into annular channel 194. A mass flow controller 196 regulatesthe flow of inert gas into inert gas duct 192.

[0042] The reaction chamber 104 includes a main chamber 200. Reactantsupply system 102 connects to the main chamber 200 at injection nozzle202. The end of injection nozzle 202 has an annular opening 204 for thepassage of inert shielding gas, and a rectangular slit 206 for thepassage of reactants to form a reactant stream in the reaction chamber.The end of injection nozzle 202 can be seen in the lower insert ofFIG. 1. Annular opening 204 has, for example, a diameter of about 1.5inches and a width along the radial direction from about ⅛ in to about{fraction (1/16)} in. The flow of shielding gas through annular opening204 helps to prevent the spread of the reactants and product particlesthroughout reaction chamber 104.

[0043] Tubular sections 208, 210 are located on either side of injectionnozzle 202. Tubular sections 208, 210 include ZnSe windows 212, 214,respectively. Windows 212, 214 are about 1 inch in diameter. Windows212, 214 are preferably cylindrical lenses with a focal length equal tothe distance between the center of the chamber to the surface of thelens to focus the beam to a point just below the center of the nozzleopening. Windows 212, 214 preferably have an antireflective coating.Appropriate ZnSe lenses are available from Janos Technology, Townshend,Vt. Tubular sections 208, 210 provide for the displacement of windows212, 214 away from main chamber 200 such that windows 212, 214 are lesslikely to be contaminated by reactants or products. Window 212, 214 aredisplaced, for example, about 3 cm from the edge of the main chamber200.

[0044] Windows 212, 214 are sealed with a rubber o-ring to tubularsections 208, 210 to prevent the flow of ambient air into reactionchamber 104. Tubular inlets 216, 218 provide for the flow of shieldinggas into tubular sections 208, 210 to reduce the contamination ofwindows 212, 214. Tubular inlets 216, 218 are connected to inert gassource 190 or to a separate inert gas source. In either case, flow toinlets 216, 218 preferably is controlled by a mass flow controller 220.

[0045] Laser 108 is aligned to generate a laser beam 222 that enterswindow 212 and exits window 214. Windows 212, 214 define a laser lightpath through main chamber 200 intersecting the flow of reactants atreaction zone 224. After exiting window 214, laser beam 222 strikespower meter 226, which also acts as a beam dump. An appropriate powermeter is available from Coherent Inc., Santa Clara, Calif. Laser 108 canbe replaced with an intense conventional light source such as an arclamp. A conventional light source preferably produces considerableamount of infrared light. Preferably, laser 108 is an infrared laser,especially a CW CO₂ laser such as an 1800 watt maximum power outputlaser available from PRC Corp., Landing, N.J.

[0046] Reactants passing through slit 206 in injection nozzle 202initiate a reactant stream. The reactant stream passes through reactionzone 224, where reaction involving the lithium precursor compound andthe manganese precursor compound takes place. Heating of the gases inreaction zone 224 is extremely rapid, roughly on the order of 105 degreeC./sec depending on the specific conditions. The reaction is rapidlyquenched upon leaving reaction zone 224, and particles 228 are formed inthe reactant/product stream. The nonequilibrium nature of the processallows for the production of nanoparticles with a highly uniform sizedistribution and structural homogeneity.

[0047] The path of the reactant\product stream continues to collectionnozzle 230. Collection nozzle 230 is spaced about 2 cm from injectionnozzle 202. The small spacing between injection nozzle 202 andcollection nozzle 230 helps reduce the contamination of reaction chamber104 with reactants and products. Collection nozzle 230 has a circularopening 232. Circular opening 232 feeds into collection system 106. Theend of collection nozzle 230 can be seen in the upper insert of FIG. 1.

[0048] The chamber pressure is monitored with a pressure gauge attachedto the main chamber. The preferred chamber pressure for the productionof the desired oxides generally ranges from about 80 Torr to about 500Torr.

[0049] Reaction chamber 104 has two additional tubular sections notshown. One of the additional tubular sections projects into the plane ofthe sectional view in FIG. 2, and the second additional tubular sectionprojects out of the plane of the sectional view in FIG. 2. When viewedfrom above, the four tubular sections are distributed roughly,symmetrically around the center of the chamber. These additional tubularsections have windows for observing the inside of the chamber. In thisconfiguration of the apparatus, the two additional tubular sections arenot used to facilitate production of particles.

[0050] Collection system 106 includes a curved channel 270 leading fromcollection nozzle 230. Because of the small size of the particles, theproduct particles follow the flow of the gas around curves. Collectionsystem 106 includes a filter 272 within the gas flow to collect theproduct particles. A variety of materials such as Teflon, glass fibersand the like can be used for the filter as long as the material is inertand has a fine enough mesh to trap the particles. Preferred materialsfor the filter include, for example, a glass fiber filter from ACE GlassInc., Vineland, N.J. and cylindrical polypropylene filters fromCole-Parmer Instrument Co., Vernon Hills, Ill.

[0051] Pump 274 is used to maintain collection system 106 at a selectedpressure. A variety of different pumps can be used. Appropriate pumpsfor use as pump 274 include, for example, Busch Model B0024 pump fromBusch, Inc., Va. Beach, Va. with a pumping capacity of about 25 cubicfeet per minute (cfm) and Leybold Model SV300 pump from Leybold VacuumProducts, Export, Pa. with a pumping capacity of about 195 cfm. It maybe desirable to flow the exhaust of the pump through a scrubber 276 toremove any remaining reactive chemicals before venting into theatmosphere. The entire apparatus 100 can be placed in a fume hood forventilation purposes and for safety considerations. Generally, the laserremains outside of the fume hood because of its large size.

[0052] The apparatus is controlled by a computer. Generally, thecomputer controls the laser and monitors the pressure in the reactionchamber. The computer can be used to control the flow of reactantsand/or the shielding gas. The pumping rate is controlled by a valve 278such as a manual needle valve or an automatic throttle valve insertedbetween pump 274 and filter 272. As the chamber pressure increases dueto the accumulation of particles on filter 272, valve 278 can beadjusted to maintain the pumping rate and the corresponding chamberpressure.

[0053] The reaction can be continued until sufficient particles arecollected on filter 272 such that the pump can no longer maintain thedesired pressure in the reaction chamber 104 against the resistancethrough filter 272. When the pressure in reaction chamber 104 can nolonger be maintained at the desired value, the reaction is stopped, andthe filter 272 is removed. With this embodiment, about 1-300 grams ofparticles can be collected in a single run before the chamber pressurecan no longer be maintained. A single run generally can last up to about10 hours depending on the type of particle being produced and the typeof filter being used.

[0054] The reaction conditions can be controlled relatively precisely.The mass flow controllers are quite accurate. The laser generally hasabout 0.5 percent power stability. With either a manual control or athrottle valve, the chamber pressure can be controlled to within about 1percent.

[0055] The configuration of the reactant supply system 102 and thecollection system 106 can be reversed. In this alternativeconfiguration, the reactants are supplied from the top of the reactionchamber, and the product particles are collected from the bottom of thechamber. In this configuration, the collection system may not include acurved section so that the collection filter is mounted directly belowthe reaction chamber.

[0056] An alternative design of a laser pyrolysis apparatus has beendescribed. See, copending and commonly assigned U.S. patent applicationSer. No. 08/808,850, now U.S. Pat. No. 5,958,348, entitled “EfficientProduction of Particles by Chemical Reaction,” incorporated herein byreference. This alternative design is intended to facilitate productionof commercial quantities of particles by laser pyrolysis. Theintroduction of aerosol reactants into this alternative apparatus designis described in copending and simultaneously filed U.S. patentapplication Ser. No. 09/188,670, now U.S. Pat. No. 6,193,936 to Gardneret al., entitled “Reactant Delivery Apparatuses,” incorporated herein byreference. The production of manganese oxide particles using thisalternative design of the reaction chamber with an aerosol deliverysystem is described in commonly assigned and simultaneously filed U.S.patent application Ser. No. 09/188,770, now U.S. Pat. No. 6,506,493 toKumar et al., entitled “Metal Oxide Particles,” incorporated herein byreference.

[0057] In general, the alternative apparatus includes a reaction chamberdesigned to reduce contamination of the chamber walls, to increase theproduction capacity and to make efficient use of resources. Toaccomplish these objectives, an elongated reaction chamber is used thatprovides for an increased throughput of reactants and products without acorresponding increase in the dead volume of the chamber. The deadvolume of the chamber can become contaminated with unreacted compoundsand/or reaction products.

[0058] The design of the improved reaction chamber 300 is schematicallyshown in FIG. 3. A reactant inlet 302 enters the main chamber 304.Reactant inlet 302 conforms generally to the shape of main chamber 304.Main chamber 304 includes an outlet 306 along the reactant/productstream for removal of particulate products, any unreacted gases andinert gases. Tubular sections 320, 322 extend from the main chamber 304.Tubular sections 320, 322 hold windows 324, 326 to define a laser beampath 328 through the reaction chamber 300. Tubular sections 320, 322 caninclude shielding gas inlets 330, 332 for the introduction of shieldinggas into tubular sections 320, 322. Shielding gas can also be introducedthrough shielding gas inlets around the reactant inlet to form a blanketof shielding gas around the reactant stream.

[0059] Referring to FIG. 4, a specific embodiment of a laser pyrolysisreaction system 350 with aerosol reactant delivery includes reactionchamber 352, a particle collection system 354, laser 356 and a reactantdelivery apparatus. A variety of embodiments of the reactant deliveryapparatuses can be used to provide aerosol reactants. One embodiment ofa reactant delivery apparatus 358 to delivery an aerosol is depicted inFIG. 5. Additional embodiments of aerosol delivery apparatuses for usewith reactant chamber 252 are described in copending and simultaneouslyfiled U.S. patent application Ser. No. 09/188,670, now U.S. Pat. No.6,193,936 to Gardner et al., entitled “Reactant Delivery Apparatuses,”incorporated herein by reference. The reactant delivery apparatus may ormay not provide an aerosol that is elongated along the elongateddimension of reaction chamber 352.

[0060] Reaction chamber 352 includes reactant inlet 364 at the bottom ofreaction chamber 352. In this embodiment, the reactants are deliveredfrom the bottom of the reaction chamber while the products are collectedfrom the top of the reaction chamber. The configuration can be reversedwith the reactants supplied from the top and product collected from thebottom, if desired. Reactant delivery apparatus 358 is connected to thereaction chamber at reactant inlet 364.

[0061] For the performance of laser pyrolysis based reaction synthesis,the aerosol generally is mixed with one or more additional reactantgases, a laser absorbing gas if the reactants do not sufficiently absorbthe laser radiation, and, optionally, an inert gas. The gases can besupplied from a pressurized cylinder or other suitable container. Inaddition, multiple reactants can be mixed in the liquid phase anddelivered as the aerosol.

[0062] Reaction chamber 352 is elongated along one dimension denoted inFIG. 4 by “w”. A laser beam path 366 enters the reaction chamber througha window 368 displaced along a tube 370 from the main chamber 372 andtraverses the elongated direction of the reaction chamber. The laserbeam passes through tube 374 and exits window 376 and terminates at beamdump 378. In operation, the laser beam intersects a reactant streamgenerated through reactant inlet 364.

[0063] The top of main chamber 372 opens into particle collection system354. Particle collection system 354 includes outlet duct 380 connectedto the top of main chamber 372 to receive the flow from main chamber372. Outlet duct 380 carries the product particles out of the plane ofthe reactant stream to a cylindrical filter within compartment 382.Compartment 382 is connected to a pump through port 384. The filterblocks flow from duct 380 to port 384 such that particles within theflow are collected on the filter.

[0064] Referring to FIG. 5, reactant delivery apparatus 358 includes anaerosol generator 482 is supported by mount 484 and a cap 486. Reactantdelivery apparatus 358 is secured to reactant inlet 364 to extend withinmain chamber 372 of FIG. 4. Mount 484 is connected to a base plate 488.Base plate 488 is fastened to reactant inlet 364 with bolts 490. Ano-ring or the like, suitably shaped, can be placed within hollow 492 toform a seal between base plate 488 and reactant inlet 364.

[0065] As noted above, properties of the product particles can bemodified by further processing. In particular, lithiated manganese oxidenanoscale particles can be heated in an oven in an oxidizing environmentor an inert environment to alter the oxygen content, to change thecrystal lattice, or to remove adsorbed compounds on the particles toimprove the quality of the particles.

[0066] The use of sufficiently mild conditions, i.e., temperatures wellbelow the melting point of the particles, results in modification of thelithiated manganese oxide particles without significantly sintering theparticles into larger particles. The processing of metal oxide nanoscaleparticles in an oven is discussed further in copending and commonlyassigned, U.S. patent application Ser. No. 08/897,903, now U.S. Pat. No.5,989,514, filed Jul. 21, 1997, entitled “Processing of Vanadium OxideParticles With Heat,” incorporated herein by reference.

[0067] A variety of apparatuses can be used to perform the heatprocessing. An example of an apparatus 700 to perform this processing isdisplayed in FIG. 6. Apparatus 700 includes a tube 702 into which theparticles are placed. Tube 702 is connected to a reactant gas source 704and inert gas source 706. Reactant gas, inert gas or a combinationthereof are placed within tube 702 to produce the desired atmosphere.

[0068] Preferably, the desired gases are flowed through tube 702.Appropriate reactant gases to produce an oxidizing environment include,for example, O₂, O₃, CO, CO₂ and combinations thereof. The reactant gascan be diluted with inert gases such as Ar, He and N₂. The gases in tube702 can be exclusively inert gases if an inert atmosphere is desired.The reactant gases may not result in changes to the stoichiometry of theparticles being heated.

[0069] Tube 702 is located within oven or furnace 708. Oven 708maintains the relevant portions of the tube at a relatively constanttemperature, although the temperature can be varied systematicallythrough the processing step, if desired. Temperature in oven 708generally is measured with a thermocouple 710. The lithiated manganeseoxide particles can be placed in tube 702 within a vial 712. Vial 712prevents loss of the particles due to gas flow. Vial 712 generally isoriented with the open end directed toward the direction of the sourceof the gas flow.

[0070] The precise conditions including type of oxidizing gas (if any),concentration of oxidizing gas, pressure or flow rate of gas,temperature and processing time can be selected to produce the desiredtype of product material. The temperatures generally are mild, i.e.,significantly below the melting point of the material. The use of mildconditions avoids interparticle sintering resulting in larger particlesizes. Some controlled sintering of the particles can be performed inoven 708 at somewhat higher temperatures to produce slightly larger,average particle diameters.

[0071] For the processing of lithiated manganese oxide, for example, thetemperatures preferably range from about 50° C. to about 600° C. andmore preferably from about 50° C. to about 550° C. The particlespreferably are heated for about 5 minutes to about 100 hours. Someempirical adjustment may be required to produce the conditionsappropriate for yielding a desired material.

[0072] B. Particle Properties

[0073] A collection of particles of interest preferably has an averagediameter for the primary particles of less than about 250 nm, preferablyfrom about 5 nm to about 100 nm, more preferably from about 5 nm toabout 50 nm. The primary particles usually have a roughly sphericalgross appearance. Upon closer examination, crystalline lithiatedmanganese oxide particles generally have facets corresponding to theunderlying crystal lattice. Nevertheless, the primary particles tend toexhibit growth that is roughly equal in the three physical dimensions togive a gross spherical appearance. Generally, 95 percent of the primaryparticles, and preferably 99 percent, have ratios of the dimension alongthe major axis to the dimension along the minor axis less than about 2.Diameter measurements on particles with asymmetries are based on anaverage of length measurements along the principle axes of the particle.

[0074] Because of their small size, the primary particles tend to formloose agglomerates due to van der Waals and other electromagnetic forcesbetween nearby particles. Nevertheless, the nanometer scale of theprimary particles is clearly observable in transmission electronmicrographs of the particles. The particles generally have a surfacearea corresponding to particles on a nanometer scale as observed in themicrographs. Furthermore, the particles can manifest unique propertiesdue to their small size and large surface area per weight of material.For example, TiO₂ nanoparticles generally exhibit altered absorptionproperties based on their small size, as described in copending andcommonly assigned U.S. patent application Ser. No. 08/962,515, now U.S.Pat. No. 6,099,798, entitled “Ultraviolet Light Block and PhotocatalyticMaterials,” incorporated herein by reference.

[0075] Laser pyrolysis, as described above, generally results inparticles having a very narrow range of particle diameters. With aerosoldelivery, the distribution of particle diameters is particularlysensitive to the reaction conditions. Nevertheless, if the reactionconditions are properly controlled, a very narrow distribution ofparticle diameters can be obtained with an aerosol delivery system asdescribed above. The primary particles preferably have a high degree ofuniformity in size. When mixed phase materials are formed, it issometimes observed that each phase has a separate narrow sizedistribution such that the mixed phase materials overall involvesmultiple overlapping narrow distributions.

[0076] As determined from examination of transmission electronmicrographs, the primary particles of a single phase and possiblymultiple phases generally have a distribution in sizes such that atleast about 95 percent, and preferably 99 percent, of the primaryparticles have a diameter greater than about 40 percent of the averagediameter and less than about 160 percent of the average diameter.Preferably, the primary particles have a distribution of diameters suchthat at least about 95 percent of the primary particles have a diametergreater than about 60 percent of the average diameter and less thanabout 140 percent of the average diameter.

[0077] Furthermore, in preferred embodiments essentially no primaryparticles have an average diameter greater than about 4 times theaverage diameter and preferably 3 times the average diameter, and morepreferably 2 times the average diameter. In other words, the particlesize distribution effectively does not have a tail indicative of a smallnumber of particles with significantly larger sizes. This is a result ofthe small reaction region and corresponding rapid quench of theparticles. An effective cut off in the tail indicates that there areless than about 1 particle in 106 have a diameter greater than aparticular cut off value above the average diameter. The narrow sizedistributions, lack of a tail in the distributions and the roughlyspherical morphology can be exploited in a variety of applications.Also, crystalline lithiated manganese oxide particles produced byannealing (heating) particles made by laser pyrolysis have a high degreeof crystallinity.

[0078] Lithium manganese oxide is known to exist in a variety ofoxidation states and several crystalline phases corresponding to theunderlying crystal structure of the manganese oxide and the degree oflithium intercalation. The phase diagram of lithiated manganese oxide isextremely complex. The manganese oxygen ratio can vary from 1:1 to 1:2.Also, the ratio of lithium to manganese, i.e., the amount of lithiumintercalated into the manganese oxide lattice, can vary from 0 to 2:1.Also, for a given stoichiometry such as LiMn₂O₄, the crystal structurecan be a cubic spinel or other crystal structures. Different portions ofthe vast phase diagram can be explored by varying the processingparameters.

EXAMPLES Example 1 Laser Pyrolysis; Aerosol Metal Precursors

[0079] The synthesis of magnesium oxide/lithiated manganese oxideparticles described in this example was performed by laser pyrolysis.The particles were produced using essentially the laser pyrolysisapparatus of FIG. 1, described above, using the reactant deliveryapparatus of FIG. 2.

[0080] The manganese chloride (Alfa Aesar, Inc., Ward Hill, Mass.)precursor and lithium chloride (Alfa Aesar, Inc.) precursor weredissolved into deionized water. The aqueous solution had a concentrationof 4 molar LiCl and 4 molar MnCl₂. The aqueous solution with the twometal precursors was carried into the reaction chamber as an aerosol.C₂H₄ gas was used as a laser absorbing gas, and Argon was used as aninert gas. O₂, Ar and C₂H₄ were delivered into the gas supply tube ofthe reactant supply system. The reactant mixture containing MnCl₂, LiCl,Ar, O₂ and C₂H₄ was introduced into the reactant nozzle for injectioninto the reaction chamber. The reactant nozzle had an opening withdimensions of ⅝ in.×{fraction (1/16)} in. Additional parameters of thelaser pyrolysis synthesis relating to the particles of Example 1 arespecified in Table 1. TABLE 1 {PRIVATE} 1 Crystal Structure AmorphousPressure (Torr) 450 Argon-Window (SCCM) 700 Argon-Shielding (SLM) 5.6Ethylene (SLM) 1.27 Argon (SLM) 1.46 Oxygen (SLM) 1.07 Laser Output(Watts) 590 Li Precursor 4 M Lithium Chloride Mn Precursor 4 M ManganeseChloride Precursor Temperature °C. Room Temperature

[0081] The production rate of manganese oxide/lithiated manganese oxideparticles was typically about 1 g/hr. To evaluate the atomicarrangement, the samples were examined by x-ray diffraction using theCu(Ka) radiation line on a Siemens D500 x-ray diffractometer. X-raydiffractograms for a sample produced under the conditions specified inTable 1 is shown in FIG. 7. The x-ray diffractogram shown in FIG. 7indicates that the sample was amorphous. In particular, a broad peakfrom about 27° to about 35° corresponds to the amorphous lithiatedmanganese oxide. A sharp peak at about 15° is due to the presence of atrace amount of manganese chloride contamination. A sharp peak at 53° isdue to a trace amount of an unidentified contaminant.

Example 2 Heat Treatment

[0082] A sample of manganese oxide/lithiated manganese oxidenanoparticles produced by laser pyrolysis according to the conditionsspecified in the Example 1 were heated in an oven under oxidizingconditions. The oven was essentially as described above with respect toFIG. 6. Between about 100 and about 300 mg of nanoparticles were placedin an open 1 cc vial within the quartz tube projecting through the oven.Oxygen gas was flowed through a 1.0 inch diameter quartz tube at a flowrate of 308 cc/min. The oven was heated to about 400° C. The particleswere heated for about 16 hours.

[0083] The crystal structure of the resulting heat treated particleswere determined by x-ray diffraction. The x-ray diffractogram for heatedsample is shown in FIG. 8. The x-ray diffractogram shown in FIG. 8indicates that the collection of particles involved mixed phase materialwith major components of LiMn₂O₄ (about 60% by volume) and Mn₃O₄ (about30% by volume) and a minor component of Mn₂O₃ (about 10% by volume). TheLiMn₂O₄ compound has a cubic spinel crystal structure. It is possiblethat the sample included additional amorphous phases of materials. Inparticular, based on the amount of lithium introduced in the reactantstream, the sample presumably contains additional lithium that is notidentified in the crystalline phases.

[0084] The embodiments described above are intended to be illustrativeand not limiting. Additional embodiments are within the claims. Althoughthe present invention has been described with reference to preferredembodiments, workers skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scopeof the invention.

What is claimed is:
 1. A method of producing composite metal oxideparticles, the method comprising reacting a reactant stream to form,within the flow of the reactant stream, a powder of composite metaloxide particles with an average diameter less than about 500 nanometers,the reactant stream comprising a first metal compound precursor and asecond metal compound precursor, wherein the reaction is driven by heatfrom a light beam and wherein the light beam intersects the reactantstream at a reaction zone.
 2. The method of claim 1 wherein thecomposite metal oxide comprises lithiated manganese oxide.
 3. The methodof claim 1 wherein the composite metal oxide comprises lithiatedvanadium oxide.
 4. The method of claim 1 wherein a metal precursorcomprises a compound selected from the group consisting of MnCl₂ andMnNO₃.
 5. The method of claim 1 wherein a metal precursor comprises acompound selected from the group consisting of LiCl and Li₂NO₃.
 6. Themethod of claim 1 wherein a metal precursor comprises VOCl₂.
 7. Themethod of claim 7 wherein the light beam is generated by an infraredlaser.
 8. The method of claim 1 wherein the reaction is performed in areaction chamber, the chamber having a cross section along a directionperpendicular to a reactant stream with a dimension along a major axisgreater than a factor of about two larger than a dimension along a minoraxis.
 9. The method of claim 1 wherein the precursor comprises a thirdmetal precursor.
 10. The method of claim 1 wherein the reactant streamcomprises an aerosol of the first metal precurosr and a vapor of thesecond metal precursor.
 11. The method of claim 1 wherein the reactantstream comprises an aerosol.
 12. The method of claim 11 wherein theaerosol is generated by a mechanical atomization aerosol generator. 13.The method of claim 1 wherein the reaction stream further comprises O₂.14. The method of claim 1 wherein the composite metal oxide particleshave an average diameter less than about 250 nm.
 15. The method of claim1 wherein the composite metal oxide particles have an average diameterless than about 100 nm.
 16. The method of claim 1 wherein the compositemetal oxide particles have essentially no particles with a diametergreater than about 4 times the average diameter.
 17. A method ofproducing composite metal oxide particles, the method comprisingreacting a reactant stream to form, within the flow of the reactantstream, a powder of composite metal oxide particles with an averagediameter less than about 500 nanometers, the reactant stream comprisinga first metal compound precursor, a second metal compound precursor anda third metal compound percursor.
 18. The method of claim 17 wherein thereaction is driven by heat from a light beam and wherein the light beamintersects the reactant stream at a reaction zone.
 19. The method ofclaim 17 wherein the reactant stream comprises an aerosol.
 20. Themethod of claim 17 wherein the first metal precursor comprises lithium,the second metal precursor comprises manganese.